Preparation of aromatic petroleum concentrate of reduced sulfur content



Nov. 3, 1959 c, HOLDER ET AL 2,911,354

' PREPARATION OF AROMATIC PETROLEUM CONCENTRATE OF REDUCED SULFURCONTENT Filed Dec. 21, 1954 CRUDE STILL OIL H Clinton H. Holder ChesterL. Read By @f/fi d/ Attorney CRUDE Inventors PREPARATION OF AROMATICPETROLEUM {oN- CENTRATE F REDUCED SULFUR CONTENT Clinton H. Holder andChester L. Read, Westfield, NJ., assignors to Esso Research andEngineering Company,- a corporation of Delaware Application December 21,1954, Serial No. 476,776

. 1 Claim. (e1. 208-96) This invention relates to the preparation ofcondensed ring aromatic petroleum concentrates andv particularly to thepreparation of such concentrates which have a moderately low sulfurcontent, i.e., about 0.8% or less sulfur content by weight. g

Condensed ring aromatic concentrates are'particularly useful as a fluxoil for coal tar burned as fuel in open hearth furnaces and the like. Ahighly aromatic material is particularly desirable for such applicationsin that the luminosity of the flame produced increases with aromaticcontent. Highly luminous 'fiames are very desirable in reverberatingfurnaces or the like. f In addition, such materials may be employed inmaking electrode coke for the aluminumindustry and-as intermediates inthemanufac- ,ture of various chemicals such as acids. derived fromcondensed ring aromatic compounds. They may. also be used as heatexchange media. In the'past thepr'eparation of such materials frompetroleum distillates has been made difiicult due to the fact that. therequirements of the steel and aluminum industries necessitate theproduction of material having a fairly low sulfur content. This isnecessary to avoid absorption of sulfur by the metallic charge in thefurnace. While numerous processes exist for the reduction'of sulfurcontent in variouspetroleum distillates to, a satisfactory level, mostoftheseprocesses involve a hydrogenation reaction which converts thesulfur to hydrogen sulfide and at the same time results in thehydrogenation of the aromatic compounds. In addition, sulfur is veryoften associated with aromatic rings so that highly aromaticconcentrates generally contain large amounts of sulfur. It has beenpossible, therefore, to produce an aromatic concentrate of low sulfurcontent only where the concentration of aromatics was relatively low.

It is an object of this invention to provide a process whereby acondensed ringaromatic concentrate derived from petroleum and havingboth a low sulfur content and.

a high concentration of aromatics may be produced."

It is a further object of this invention to provide a process wherebycatalytically crackedcycle stock may 'be converted to a relatively lowsulfur-contentaromatic concentrate without hydrogenationof the aromaticcontent thereof.

These and other objects, whichwill be in part apparent and in partspecifically pointed out in the ensuing description, are attained bydistillingia' crude oil to produce a fraction boiling above aboutf600?F., subjecting this fraction to catalytic cracking, segregating thecracked products to form a fraction boiling in thesame range as theoriginal distillate, subjecting this cracked stock to a solventextraction process in orderv to segregate aromatic compounds, and thencontacting the aromatic concentrate produced by this extraction processwith hydrogen in the presence of a catalyst in order to reduce thesulfur content. of the concentrate.

Ithas been found that in order toproduce a satisfac- 2,911,354 IPatented Nov. .3, 1959 distilled from the crude oil be subjected tocatalytic cracking. Prior to cracking the gasoil fraction normallycontains less than 25% by weight of aromatics. This step is believed tocause the dehydrogenation of naphthenes so that the aromatics in thecatalytica'lly cracked cycle stock are in a form relatively easilyseparable by conventional solvent extraction processes such asextraction with phenol, liquid' sulfur dioxide, or furfural. Most of thesulfur in the feed stock tends to concentrate'itself in the aromaticphase so that the feed for thehydrodesulfurization step isofsubstantially higher sulfur content than the original' crude. Thehydrodesulfurization step of the process must becarried out undersufiiciently severe conditions to materially reduce the sulfur contentof the aromatic concentrate, but the reaction conditions must not figureof drawings, which is a diagrammatic representation of aprocessembodying the present invention.

The drawing shows a conventional crude still v10 into which crude oil isintroduced through line 11. Heavy residualpro'ducts are removed from thebottom of the still at 12, while light fractions are taken off overheadthrough line 13. Thepresent invention is concerned with the processingof that fraction boiling in' the range; of about 600 F. to about 1200 P.which is removed from the still through line 14and passestothecatalyt-ic cracking unit 15. In the catalytic cracking unit-thefeedstock is cracked under conditions well known to the art and forms ahydrocarbon mixture containing a substantial concentration of aromaticcompounds. As previously stated; these aromatic compoundsareparticularly-well adapted .to solvent separation from, the aliphaticC Ol'l-- stituents of the cracking stock and are peculiar 'tocatalyticas opposed to thermal cracking. For this reason the cracking operation:carried out in unit 15 must be of a catalytic nature. Any conventionalcatalytic cracking system adapted to convert hydrocarbons into materialsof a lower boiling range may be employed. The process may beof acontinuousor batch operation. in fixed bed, moving bed, fluid orsuspensoid systems. Heat required for cracking may besupplied. aspreheat of the distillate and/or as sensible heat of exothermicallyregenerated catalyst,.or in any other conventional. manner. Modifiednatural orsynthetic clay or gel type catalysts such as silica-aluminacomposites or other conventional cracking catalysts may be employed attemperatures of about 800.-1000 F. and at pressures of from aboutatmospheric to about 25 p.s.i.g., all in a manner well known to the art.

The cracked cycle stock is passed from the cracker 15 via line 16 to thestill 17. There the cracked hydro- 7 carbon mixture is separated into alight. fraction taken off overhead at 18, a heavy residual fractiontaken oif'at 19, and a fraction. boiling in approximately the same rangeas the feed stock for the catalytic cracking operation, namely, 600l200F; This fraction,.referred to as catalytically cracked cycle stock, istaken off via line 20 and passed to the extraction tower 21. Forpurposes of illustration it will be assumed that the extractionoperationcarried out in tower 21 utilizes phenol as a solvent for thearomatics in the feed stock. However, it is to be understood that phenolis specified only for the purpose .of illustration and thatother.solvents exhibiting .i- 3 similar selectivity for aromatics, such asliquid sulfur dioxide, nitrobenzene, aniline, cresol, and furfural, maybe employed with equal facility. The phenol extracts thearomaticcontentof the catalytically cracked cycle stock in a manner well knownto the art, forming an extract phase in which the aromatics areconcentrated and a raffinate phase relatively poor in aromatics, which 4the original crude oil. In order to prepare a concentrate suitable foruse as flux oil or the like, it is necessary to effect a substantialreduction in the sulfur content of this aromatic extract, i.e., toreduce the sulfur content to a level not higher than about 0.8% byweight. It is well known in the petroleum refining art to reduce thesulfur content of various hydrocarbon fractions by contacting them withhydrogen under suitable conditions in latter is taken off through line22 and passed to a suitable solvent recovery system not shown. Theextract containing the aromatics passes via line 23 to the stripper 24,wherein solvent is separated from the aromatic hydrocarbon concentrate,the solvent being removed overhead through line 25 while the aromaticconcentrate is removed via line 26. 7

As pointed out above, the aromatics produced during catalytic crackingare particularly adapted to separation by solvent extraction. Inaddition to this, the operation of catalytic cracking itself increasesthe content of condensed ring aromatic compounds. A comparison is setforth below, illustrating'the concentration by weight of compoundscontaining aromatic rings in various extraction cuts madelby the phenolextraction of a typical cracked cycle stock and a typical virgin lubedistillate. From this comparison it is seen that the concentration ofaromatics is considerably greater for the same yield when extractingcycle stock than when extracting the virgin distillate.

The efficiency of the extraction process may be con-.

' trolled by varying temperature, amount of solvent employed, etc. Forexample, at extraction temperatures of 125 l90 F. using phenol modifiedby 1-10% of water, the following relation exists between extract yieldand amount of phenol employed.

Percent Extract Yield, Percent Solvent on Feed by Volume It will beappreciated from the above that extracts of order to convert the sulfurto hydrogen sulfide. In some cases the hydrogen is supplied by thedehydrogenation of various constituents of the hydrocarbon fraction.Such a hydrodesulfurization method is unsuitable for the treatment ofhighly aromatic stocks, however, and it has been found necessary toutilize a hydrodesulfurization step in which the hydrogen is suppliedfrom an external source rather than by dehydrogenation of thehydrocarbon constituents being treated.

Accordingly, the hydrodesulfurization of the aromatic concentrate iscarried out in reactor 27, into which hydrogen is introduced via line28. The hydrogen and the aromatic concentrate must be contacted in thepresence of a catalyst in order to produce the desired reaction.Numerous catalysts which will effect this result are known to therefining art, and any of these wellknown methods may be employed inreactor 27 in accordance. with the present invention. It has been found,however, that most beneficial results, from the standpoint of reducingsulfur content and of retaining a relatively high level of aromaticity,are obtained when a cobalt molybdate catalyst is employed. Catalystsmade up of from 324% by weight of cobalt molybdate supported on A1 0 andpreferably containing about 15% by weight of cobalt molybdate, areparticularly suitable. Mixtures of cobalt and molybdenum oxides may beemployed instead of cobalt molybdate. Other desulfurizing catalysts thatmay be employed include platinum (up to about 2%) supported on aluminaand molybdenum oxide-alumina compositions. The contacting may be carriedout utilizing a fixed bed technique,

or in any other conventional manner.

In order to minimize or substantially prevent the hydrogenation of thearomatic compounds in the concentrate while the hydrodesulfurizationreaction is taking place, it is necessary to carefully control theconditions existing within the hydrodesulfurization unit 27. In general,the hydrodesulfurization conditions must be kept relatively mild, thatis, factors which would tend to cause hydrogenation of the aromaticsmust be maintained near theirminimum limits. These factors aretemperature,

sufiiciently high aromatics concentration can be pre pared using fromabout 75% to about 200% by volume of phenol based on feed.

The above comparison illustrates the advantages of using catalyticallycracked cycle stock as a feed material to the hydrodesulfurizationprocess and also that more highly concentrated aromatic feeds may beobtained when operating the extraction process at relatively lowAlthough the concentrate leaving the stripper through line 26 is rich incondensed ring aromatics and there-1v;

fore of potential value as aflux oil, etc., it may have a sulfurconcentration as great as or greater than thatof pressure, and ratio ofhydrogen to aromatic concentrate employed. A suitable temperature rangehas been found to be from about 600 F. to 800 F., and preferably from650 F. to 750 F- Pressures in the hydrodesulfurization unit should bekept at about 50 to 500 psig, with a preferred range of 300-500p.s.i.g., and the gas rate from about 400 to about 4000 cubic feet ofhydrogen per barrel of feed.

The concentrate is withdrawn from the hydrodesulfurization unit 27 vialine 29. This concentrate, in addition to being'useful as a flux oil forcoal tar or other reverberatoryfurnace fuels, may also serve as astarting material for the manufacture of various condensed aromatic ringcompounds. Specific aromatic compounds or types of compounds may beisolated from this stream and used for any desired purpose.

The hydrodesulfurization catalyst may become coated with carbon after anextended period of use. Such a deposit may be removcd by a suitableoxidizing procedure, and the catalyst may then be regenerated accordingto any technique known to the prior art.

As a specific example of the operation of the process of the presentinvention, an'aromatic concentrate having the following inspectionsobtainedfrom phenol extraction of catalytically cracked cycle stock wasemployed as a starting material.

Gravity, API 1.5 Viscosity at 100 F., S.S.U. 957.0 Viscosity at 210 F.,S.S.U. 50.3 Sulfur, weight percent 1.83 Conradson carbon, weight percent5.0 Tag Robinson color Mt Pour point, F. 45 Refractive index at 75 C.1.6434 Aniline point, F. -1 43 Aromatics by silica gel, wt. percent 92Initial boiling point, F.

Using this feed stock, two hydrodesulfurization runs were carried outusing a 15% cobalt molybdate catalyst supported on A1 0 and externallysupplied hydrogen. The conditions of these hydrodesulfurization runsareset forth in Table I below.

Table 1 Run 1 Run 2 Oil rate, volumes per volume of catalyst per hour 1.0 2. 0 Temperature, F 700 700 Total Gas Rate, Standard Cubic Feet perBarrel 3, 500 3, 500 Fresh Hydrogen Rate, Standard Cubic Feet per Barrel1, 000 1, 000 Pressure, p.s.i.g 400 400 In both cases the hydrofinedliquid was lemon yellow in color and had the following inspections setforth in Table II below.

Table 11 Run 1 Run 2 Gravity, API 1. 2 0. 8 Viscosity at 100 F. S.S.U597 Viscosity at 210 F; S.S.U 47. 4 47. 6 Sulfur, Weight Percent 0.5 0.8 Conradson Carbon, Weight Percent 3.0 3.1 Pour Point, 30 35 RefractiveIndex at 75 C- 1. 6210 1. 6241 ine Point, --22 --22 Aromatics by SilicaGel, Weight Percent" 92 90 Initial Boiling Point, F 514 439 From theabove data it will be seen that the aromatic content of the feed stock,which is expressed here in terms of the percentage of compoundscontaining an aromatic ring, was not lowered appreciably or at all underthe conditions of hydrodesulfurization employed, while the sulfurcontent was reduced very substantially to an acceptable level in each ofthe runs. The low sulfur content aromatic, concentrate thus produced isuseful as a flux oil for the burning of coal tar in open hearthfurnaces, as pointed out previously, and also as the starting materialfor the preparation of various forms of carbon such as coke for thealuminum industry and carbon black.

While the invention has been described in terms of a specific embodimentemploying a particular solvent extraction method for concentrating thecondensed ring aromatic compounds and a specific hydrodesulfurizationmethod, it is to be understood that the invention is not limited to theutilization of these specific means, but that equivalent steps known tothose skilled in the art may be substituted therefor. therefore not tobe limited except by What is claimed is:

The process of preparing a condensed ring aromatic petroleum concentrateuseful as a flux oil for burning coal tar in open hearth furnaces, saidconcentrate containing at least about weight percent aromatic compoundsand having a reduced sulfur content of less than about 0.8 weightpercent, which comprises the steps of distilling a crude petroleum oilcontaining sulfur to form a gas oil fraction boiling above about 600 F.and containing at least about 1 weight percent sulfur, catalyticallycracking said fraction to form a cracked hydrocarbon product, distillingsaid cracked hydrocarbon product to segregate a cracked fraction boilingabove about 600 F., subjecting said cracked hydrocarbon fraction to asolvent extraction to produce an extract phase rich in aromaticcompounds, recovering an aromatic hydrocarbon concentrate containing atleast about 90 weight percent of aromatic hydrocarbons from said extractphase, and contacting said aromatic concentrate at a liquid oil spacevelocity rate of 1 to 2 volumes per volume of catalyst per hour withsupported cobalt molybdate catalyst at 700 to 750 F. under a pressure of200 to 400 psig. in the presence of hydrogen gas flowing at a rate of1000 to about 3500 standard cubic feet per barrel of the aromaticconcentrate, said gas'containing fresh free hydrogen supplied from anexternal source in an amount of at least about 1000 standard cubic feetper barrel ofthe aromatic concentrate treated to reduce the sulfurcontent of the thus treated aromatic concentrate to less than about 0.8weight percent without appreciably lowering its aromatic content.

the appended claim.

References Cited in the file of this patent UNITED STATES PATENTS Thescope of the invention is

